3phase PWM variable speed motor

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I took apart a DVD-ROM drive for the heck of it and the control LSI is
amazing stuff.

The driver chip has everything to directly drive all the mechanical
parts in a CD-ROM drive from loading tray, focus, tracking, sled and
the spindle motor. I find the spindle motor control the most
fascinating.

http://www.rohm.com/products/databook/optdisc/pdf/bd7902cfs.pdf

The chip controls the spindle motor using three phase PWM and reading
the controller documentation leads me to believe the thing can be
controlled somehow with pin 24.

The range is rather wide 230RPM while playing back audio CD at outer
diameter and about 10,000RPM at 48x CAV mode. The chip can also apply
reverse torque to quickly bring the disc to stop.

Is it difficult to make a variable speed drive using the spindle motor
and the LSI pulled from a DVD-ROm drive to let me run the motor
anywhere from 280 to 10,000RPM outside of the original drive? It
would surely make a cool project part.


If this sophisticated control can be built into a $20 DVD-ROM drive,
how expensive would it be to integrate a similar controller with
beefier drive circuit to drive a motor in few hundred watt to a few
kilowatt range?

 

You are in the 19th century.The germans have used this since 1990.The ICE
train (InterCityExpress) has 13,000 HP, probably 8 traction motors and 2
"locomotives" (see www.db.de if you can read german).The motors are
asynchronous, three-phase squirrel cage and of course they must have
sufficient torque to pull the train at stop and enough rpm to reach the
maximum speed of 200 km/h.The cetenary system is 15 kV 16 2/3 Hz.Of course,
there's such a drive as in the DVD.In normal electric locomotives there's a
motor with brushes and excitation in series (like the one your drill has or
your mixer, the one you make the ice-cream) and a transformer with 18
taps.To start the train, you need high current and low voltage.For maximum
speed, you need high voltage and sufficient current.These motors are
directly coupled on the wheels.

 

The major player in answering this question is "volume"
Because the manufacturer can expect to sell millions of thses things,( DVD
rom Drives) The development cost can be split, a few dollars over each item
with no major impact in the overall price. After the development costs have
been covered the manufacturer can then turn a reasonable profit before
market saturation.

Not so with larger drives. The thing is there are a lot more "Players" in
the motor drive market and in reality, if a maunfacturer goes to market with
say a 2KW Drive there are probably more then 30 manufacturers out there each
trying for their share of a rather limited market, so the prospective sales
will be maybe only in the 1,000's and not the millions that the DVD rom
makers have at their disposal.

another factor is PC users tend to have a rather "Geeky" approach to their
equipment, with a fair market wanting the Latest and greatest, So they would
be perfectily willing to throw away a perfectly good "Widgett" to replace it
with another widgett of similar cost but more functions or better
specifications. Usually in the industrial drive market, once a device is up
and running, There it stays until it breaks or the whole machine is ready
for an upgrade.

The other thing is the DVD Rom Drives are a dedicated application, Known
Supply Voltage, Known load inertia, One job description. as we all know
the application of Variable speed AC Drives has about as many diferent jobs
and supply voltages as you immagination can put together. any reputable
drive maker must design his drive to be as adaptible as possible so that it
can be applied to any of these aapplications. This all adds Cost to the
development.

Having said that, there, is no reason why the cost of drives will not fall
as time progresses, as we learn how to do things more cost effectively and
new technology either takes away some of the obsticales or makes them easier
to contend with.

Well there's my 2cents worth.